The invention relates to environmental sensors, such as particle counters that are used to detect particles in air or liquid environments.
Environmental sensors move a fluid past a sensor for sensing an aspect of the fluid. The environmental sensor may also filter the fluid. For example, particle counters can be used to detect microscopic particles in gaseous fluids. Particle counters can be used, for example, to monitor clean environments and process gaseous fluids where contamination of a product being manufactured can render that product unsuitable for its intended purpose. Particle counters can include means of moving a measured and controlled volume of air through the sensor, a light source, collection optics, photo detector, circuitry for converting detected scattered light to electrical signals, a means of discriminating electrical signals caused by particles at the sizes of interest, and a means of counting the number of times that those signals occur over some period of time.
Pharmaceutical manufacturers maintain controlled environments that meet cleanliness standards for the maximum number of particles greater than a certain size occupying a specified volume of air. Environments where pharmaceutical products are formulated and packaged are regulated by government agencies to insure compliance to the cleanliness standards.
Semiconductor and aerospace manufacturers also monitor the cleanliness of their process fluids, gases, and environments in order to eliminate sources of contamination and increase yield. Other industries, for example those that make automotive products, micro-machined structures, and optical assemblies also monitor their environments to detect and control contamination that affects product performance and quality.
Particle counters commonly are battery powered. Exemplary battery powered particle counters using a centrifugal blower include U.S. Pat. Nos. 5,515,164; 5,600,438; RE37,353; U.S. Pat. Nos. 5,825,487; and 7,752,930 and using a regenerative centrifugal blower include U.S. Pat. No. 6,167,107, all of which are incorporated herein by reference. One or more of the patents also disclose methods and systems for incorporating blowers with the associated methods for measuring and controlling the flow rate through the sensor.
Older particle counters include positive displacement pumps with diaphragms or carbon vanes. These counters require considerably more power which made battery operation impractical for most applications that require the common flow rate of 1 CFM (cubic foot per minute). However, the use of the centrifugal blower alleviated this problem and in the years that followed, battery powered flow rates were able to increase up to 100 LPM (liters per minute), which is almost four time greater than 1 CFM. Advances in battery technology have also enabled these higher flow rate particle counters. However, the blowers used in particle counters have not advanced since the above-referenced patents were issued.
Accordingly, there is the need for a new and useful environmental sensor with an improved blower and related control.